The invention relates to a heat exchanger for heating a liquid, in particular, for high-pressure cleaners, comprising an inner and an outer heating coil which each have a plurality of turns, and comprising spacers which are arranged between the inner heating coil and the outer heating coil and are distributed over the circumference of the inner heating coil.
The invention also relates to methods for manufacturing such a heat exchanger, wherein an inner heating coil is wound from a pipe, several spacers distributed over the circumference of the inner heating coil are arranged and fixed on the outer side of the inner heating coil, and an outer heating coil is wound from the pipe onto the spacers.
Such heat exchangers are used, in particular, for heating a cleaning liquid for high-pressure cleaners. The heat exchangers form a double-pipe spiral comprising an inner and an outer heating coil. The inner heating coil defines a combustion chamber in which a fuel nozzle can be positioned. This makes it possible to ignite a flame in the combustion chamber, so that hot air flows around the heat exchanger. The cleaning liquid can flow through the heat exchanger. Heat transfer then takes place from the hot air via the heating coils to the liquid to be heated, which can then be directed at an article to be cleaned.
The heat exchangers are therefore used as continuous flow heaters. To improve the efficiency of the heat exchangers, it is proposed in EP 1 255 085 B1 that the spacers be configured in such a way with different radial recesses for the turns of the outer heating coil that the turns are arranged at least partially in radially offset relation to one another. This enables improved heat transfer from the heated air to the heating coils. However, this requires use of a large number of specially designed spacers, the positioning of which on the outer side of the inner heating coil must be carefully selected.
The object of the present invention is to provide a heat exchanger of the generic kind and a method for its manufacture, thereby enabling the heat exchanger to be manufactured more cost-effectively and to be highly efficient.